A large Norway rat discovered in a permanent trap on the ‘pest-free’ island of Motuora in the Hauraki Gulf has sparked a Department of Conservation (DOC) response operation. Motuora, which is jointly managed by DOC and the Motuora Restoration Society and is home to young kiwi chicks and other threatened species, has never had a population of mammalian predators such as rats, stoats or ferrets.

The rat was found yesterday during a regular check, caught in one of the sentry stations designed to detect and trap any invading pests. Based on the level of decay, it is estimated the animal had been dead at least a fortnight. A similar invasion in February 2008 ended with a single rat being caught after several weeks of effort.

The main concern now is the risk that other rodents may be present, prompting DOC staff and volunteers to widen the trapping programme with a large number of extra traps placed over the island. This afternoon a rodent detection dog will be deployed, a tool that has proved effective in the past.

Endangered native birds are at risk of losing their instinct to recognise and flee mammalian enemies when moved between predator-free and predator-filled sites, says a Massey researcher.

Sarah Whitwell, a biology Masters student at Massey’s Institute of Natural Resources in Albany, designed an experiment using a pulley system to dangle a stuffed stoat and morepork at nesting North Island robins to test their fear responses. She says most robins in areas free of introduced predators such as stoats failed to get into a flap at the sight of an enemy, albeit a fake version.

Her research adds to growing evidence that native birds’ responses to mammalian predators are not genetically hard-wired.

“That’s because introduced mammal predators have been here a relatively short time, whereas native birds have been here for millions of years.”

She says already endangered native bird species would be at increased risk if moved back to wilderness sites with mammalian predators after inhabiting mammal-free conservation areas without some form of predator-recognition training.

The responses of robins in predator-controlled Wenderholm Reserve and Tiritiri Matangi Island near Auckland were compared with those in the central North Island, where the birds have long co-existed with native and introduced predators.

A Norway rat found on a ferry due to sail to Tiritiri Matangi was stopped from getting to the island sanctuary due to quick action by the ferry operator.

“All we need is one pregnant rodent to come ashore on Tiritiri and we would have a major incident on our hands.”

“Endangered species on the island include birds like the saddleback, which was wiped out on other islands by rats. Tiritiri has become a sanctuary for many threatened species that could be put at risk if visitors to the island are not vigilant and pest aware.” full press release